发现问题
在io.moquette.spi.impl.BrokerInterceptor的构造函数中，新建了一个线程池，代码如下：
private BrokerInterceptor(int poolSize, List handlers) {
LOG.info("Initializing broker interceptor. InterceptorIds={}", getInterceptorIds(handlers));
this.handlers = new HashMap<>();
for (Class messageType : InterceptHandler.ALL_MESSAGE_TYPES) {
this.handlers.put(messageType, new CopyOnWriteArrayList());
}
for (InterceptHandler handler : handlers) {
this.addInterceptHandler(handler);
}
executor = Executors.newFixedThreadPool(poolSize);
} executor = Executors.newFixedThreadPool(poolSize);这句代码虽然创建了一个固定线程数量的线程池，但是线程池的任务队列并没有做限制，一旦某个InterceptHandler中的某个方法进行了耗时处理，在高并发的情况下，会很容易导致线程池的队列堆积大量待处理的任务，进而可能造成内存溢出。
解决问题
分别添加以下类和接口
public class ThreadPoolHelper {
public static ExecutorService createFixedExecutor(int threadNum,int capacity,String threadFactoryName) {
return new ThreadPoolExecutor(
threadNum,
threadNum,
30,
TimeUnit.SECONDS,
new LinkedBlockingDeque(capacity),
new SimpleThreadFactory(threadFactoryName),
new LogDiscardRejectPolicy()
);
}
}
public class SimpleThreadFactory implements ThreadFactory {
private static final String NAME_FORMAT = "%s-%s";
private String threadNamePrefix;
public SimpleThreadFactory(String threadNamePrefix) {
this.threadNamePrefix = threadNamePrefix;
}
@Override
public Thread newThread(Runnable runnable) {
Thread thread = new Thread(runnable);
thread.setName(String.format(NAME_FORMAT, threadNamePrefix, System.currentTimeMillis()));
return thread;
}
}
public class LogDiscardRejectPolicy implements RejectedExecutionHandler {
private static final Logger LOG = LoggerFactory.getLogger(LogDiscardRejectPolicy.class);
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
LOG.error("executor:{} task queue has full, runnable:{} discarded",executor,r);
if (!(r instanceof PublishTask)) {
return;
}
PublishTask publishTask = (PublishTask) r;
InterceptHandler interceptHandler = publishTask.getInterceptHandler();
if (!(interceptHandler instanceof RejectHandler)) {
return;
}
((RejectHandler)interceptHandler).rejectedExecution(r,executor);
}
}
public interface RejectHandler {
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor);
}
BrokerInterceptor 创建线程池的逻辑改为
private BrokerInterceptor(int poolSize, int capacity, List handlers) {
LOG.info("Initializing broker interceptor. InterceptorIds={}", getInterceptorIds(handlers));
this.handlers = new HashMap<>();
for (Class messageType : InterceptHandler.ALL_MESSAGE_TYPES) {
this.handlers.put(messageType, new CopyOnWriteArrayList());
}
for (InterceptHandler handler : handlers) {
this.addInterceptHandler(handler);
}
/** modify by liuhh */
executor = ThreadPoolHelper.createFixedExecutor(poolSize, capacity, THREAD_POOL_NAME);
//executor = Executors.newFixedThreadPool(poolSize);
} 解释：
（1）ThreadPoolHelper中的createFixedExecutor()方法为新建的线程池指定任务队列大小和拒绝策略LogDiscardRejectPolicy
（2）在LogDiscardRejectPolicy中，首先将被拒绝的任务log一遍，对于PublishTask（moquette改造笔记(二)：优化BrokerInterceptor notifyTopicPublished()逻辑）做特殊处理，会交给实现RejectHandler的InterceptHandler处理，由业务逻辑决定，出现任务太多处理不完被遗弃的任务该如何处理。
修改InterceptHandler的实现，实现RejectHandler接口
在 moquette改造笔记(一)：整合到SpringBoot 中修改SafetyInterceptHandler实现，添加对RejectHandler的实现如下
@Slf4j
@Component
public class SafetyInterceptHandler extends AbstractInterceptHandler{
@Override
public String getID() {
return SafetyInterceptHandler.class.getName();
}
@Override
public void onConnect(InterceptConnectMessage msg) {
}
@Override
public void onConnectionLost(InterceptConnectionLostMessage msg) {
}
@Override
public void onPublish(InterceptPublishMessage msg) {
}
@Override
public void onMessageAcknowledged(InterceptAcknowledgedMessage msg) {
}
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
/**MQTT SERVICE 负载过大，处理不过来时，会回调该方法*/
//例如可以发生邮件通知相关人员
}
}moquette改造笔记(四)：解决InterceptHandler中的onConnectionLost()调用两次